Wireless power feeder, wireless power receiver, and wireless power transmission system

ABSTRACT

To increase efficiency of wireless power feeding to a moving object in wireless power feeding of a magnetic field resonance type. A wireless power feeder includes a plurality of feeding coils and a power feeding source (power transmission control circuit) provided in common to the plurality of feeding coils and feeds power from the plurality of feeding coils to a receiving coil by wireless. The plurality of feeding coils are adjacently arranged such that coil surfaces thereof partially overlap each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless power feeding and, more particularly, to arrangement of feeding coils or receiving coils.

2. Description of Related Art

A wireless power feeding technique of feeding power without a power cord is now attracting attention. The current wireless power feeding technique is roughly divided into three: (A) type utilizing electromagnetic induction (for short range); (B) type utilizing radio wave (for long range); and (C) type utilizing resonance phenomenon of magnetic field (for intermediate range).

The type (A) utilizing electromagnetic induction has generally been employed in familiar home appliances such as an electric shaver; however, it can be effective only in a short range. The type (B) utilizing radio wave is available in a long range; however, it has small electric power. The type (C) utilizing resonance phenomenon is a comparatively new technique and is of particular interest because of its high power transmission efficiency even in an intermediate range of about several meters. For example, a plan is being studied in which a receiving coil is buried in a lower portion of an EV (Electric Vehicle) so as to feed power from a feeding coil in the ground in a non-contact manner. Hereinafter, the type (C) is referred to as “magnetic field resonance type”.

The magnetic field resonance type is based on a theory published by Massachusetts Institute of Technology in 2006 (refer to Patent Document 1). In Patent Document 1, four coils are prepared. The four coils are referred to as “exciting coil”, “feeding coil”, “receiving coil”, and “loading coil” in the order starting from the feeding side. The exciting coil and feeding coil closely face each other for electromagnetic coupling. Similarly, the receiving coil and loading coil closely face each other for electromagnetic coupling. The distance (intermediate distance) between the feeding coil and receiving coil is larger than the distance between the exciting coil and feeding coil and distance between the receiving coil and loading coil. This system aims to feed power from the feeding coil to receiving coil.

When AC power is fed to the exciting coil, current also flows in the feeding coil according to the principle of electromagnetic induction. When the feeding coil generates a magnetic field to cause the feeding coil and receiving coil to magnetically resonate, high current flows in the receiving coil. At this time, current also flows in the loading coil according to the principle of electromagnetic induction, and power is taken from a load connected in series to the loading coil. By utilizing the magnetic field resonance phenomenon, high power transmission efficiency can be achieved even if the feeding coil and receiving coil are largely spaced from each other (refer to Patent Document 2, Patent Document 3 and Patent Document 4).

CITATION LIST Patent Document

[Patent Document 1] U.S. Patent Application Publication No. 2008/0278264

[Patent Document 2] Jpn. Pat. Appln. Laid-Open Publication No. 2006-230032

[Patent Document 3] International Publication No. 2006/022365

[Patent Document 4] U.S. Patent Application Publication No. 2009/0072629

[Patent Document 5] Jpn. Pat. Appln. Laid-Open Publication No. 2010-63245

[Patent Document 6] Jpn. Pat. Appln. Laid-Open Publication No. 2011-109903

[Patent Document 7] Jpn. Pat. Appln. Laid-Open Publication No. 2009-252970

[Patent Document 8] Jpn. Pat. Appln. Laid-Open Publication No. 2009-177921

[Patent Document 9] Jpn. Pat. Appln. Laid-Open Publication No. 2011-139621

[Patent Document 10] Japanese Patent No. 4,453,741

[Patent Document 11] Jpn. Pat. Appln. Laid-Open Publication No. 2009-164293

[Patent Document 12] WO 93/023909

It has been pointed out that an EV having a charging connector that is now under consideration has poor workability in terms of handling of a connector or an electric cable. When wireless power feeding in which power is fed from a feeding coil is adopted for the EV, a connector connecting work can be eliminated, and safety can be increased. In Patent Document 10, power is fed from a primary self-resonant coil (feeding coil) in the ground to a secondary self-resonant coil (receiving coil) in the vehicle by wireless. However, in this technique, if the feeding and receiving coils are displaced from set positions, power transmission efficiency may significantly decrease.

In Patent Document 11, a plurality of feeding coils overlap each other (see FIG. 1 of Patent Document 11) so as to prevent the power transmission efficiency from excessively decreasing depending on the position of the receiving coil. In Patent document 11, wireless power feeding during moving is not assumed, and thus an AC power source is provided for each feeding coil (see FIG. 5 of Patent Document 11). Since it is necessary to arrange a large number of feeding coils in order to achieve wireless power feeding for a moving object, a configuration of Patent Document 11 in which the AC power source is provided for each feeding coil is impractical.

In Patent Document 12, power is fed from a primary inductive path obtained by connecting in series a plurality of feeding coils and an AC power source to a vehicle by wireless. In this technique, however, the vehicle receives power only when it is positioned just above the feeding coil, making it difficult to achieve stable power feeding.

An object of the present invention is to increase efficiency of wireless power feeding.

SUMMARY

A wireless power feeder according to the present invention includes a plurality of feeding coils and a power transmission control circuit provided in common to the plurality of feeding coils for supplying AC power thereto. The plurality of feeding coils are adjacently arranged such that coil surfaces thereof partially overlap each other.

A wireless power receiver according to the present invention receives, at a receiving coil, AC power fed by wireless from a feeding coil. The wireless power receiver includes a plurality of receiving coils and a loading coil provided in common to the plurality of receiving coils, magnetically coupled thereto, and receives the AC power that the plurality of receiving coils have received from the feeding coil. The plurality of receiving coils are adjacently arranged such that coil surfaces thereof partially overlap each other.

A wireless power transmission system according to the present invention is a system for feeding power from a feeding coil to a receiving coil and includes a wireless power feeder and a wireless power receiver. The wireless power feeder includes a plurality of feeding coils and a power transmission control circuit provided in common to the plurality of feeding coils for supplying AC power thereto. The wireless power receiver includes a receiving coil, a loading coil that is magnetically coupled to the receiving coil and receives the AC power that the receiving coil has received from the feeding coil, and a secondary battery connected to the loading coil. The plurality of feeding coils are adjacently arranged such that coil surfaces thereof partially overlap each other. The secondary battery is charged with the AC power supplied to the loading coil.

According to the present invention, it is possible to easily increase efficiency of wireless power feeding to a moving object.

BRIEF DESCRIPTION OF THE DRAWINGS

The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view illustrating operation principle of a wireless power transmission system in a first embodiment;

FIG. 2 is an exemplary view of the wireless power transmission system capable of feeding power to the wireless power receiver which is moving;

FIG. 3 is a view illustrating an overlapping structure of the feeding coils;

FIG. 4 is an exemplary view illustrating a state where a vehicle having the wireless power receiver receives power while moving;

FIG. 5 is an exemplary view illustrating a relationship between power to be supplied to the secondary battery and a position of the vehicle;

FIG. 6 is an exemplary view of the wireless power feeder of a parallel-feeding type;

FIG. 7 is an exemplary view of the wireless power feeder of a series-receiving type;

FIG. 8 is an exemplary view of the wireless power feeder of a parallel-receiving type;

FIG. 9 is an exemplary view illustrating a positional relationship between the receiving coil of the wireless power receiver and feeding coil of the wireless power feeder;

FIG. 10 is a view illustrating operation principle of the wireless power transmission system in a second embodiment;

FIG. 11 is a view illustrating operation principle of the wireless power transmission system in a third embodiment; and

FIG. 12 is an exemplary view of the wireless power feeder in which a plurality of feeding methods can be switched therebetween.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a view illustrating operation principle of a wireless power transmission system 100 in a first embodiment. A wireless power transmission system 100 according to the first embodiment includes a wireless power feeder 116 and a wireless power receiver 118. The wireless power feeder 116 includes a power supply circuit 110 and a feeding coil circuit 120. A power feeding LC resonance circuit 300 is formed by the feeding coil circuit 120. The wireless power receiver 118 includes a receiving coil circuit 130 and a loading circuit 140. A power receiving LC resonance circuit 302 is formed by the receiving coil circuit 130.

The power supply circuit 110 includes a power feeding source VG (power transmission control circuit) and an exciting coil L1. The feeding coil circuit 120 (power feeding LC resonance circuit 300) includes a capacitor C2 and a feeding coil L2. The receiving coil circuit 130 (power receiving LC resonance circuit 302) includes a capacitor C3 and a receiving coil L3. The loading circuit 140 includes a loading coil L4 and a load LD. The values of the capacitor C2, feeding coil L2, capacitor C3, and receiving coil L3 are set such that the resonance frequencies of the power feeding LC resonance circuit 300 and power receiving LC resonance circuit 302 coincide with each other in a state where the feeding coil L2 and receiving coil L3 are disposed away from each other far enough to ignore the magnetic field coupling therebetween. This common resonance frequency is assumed to be fr0.

In a state where the feeding coil L2 and receiving coil L3 are brought close to each other in such a degree that they can be magnetic-field-coupled to each other, a new resonance circuit is formed by the power feeding LC resonance circuit 300, power receiving LC resonance circuit 302, and mutual inductance generated between them. The new resonance circuit has two resonance frequencies fr1 and fr2 (fr1<fr0<fr2) due to the influence of the mutual inductance. When the wireless power feeder 116 supplies AC power from a power feeding source VG to the power feeding LC resonance circuit 300 at the resonance frequency fr1, the power feeding LC resonance circuit 300 constituting a part of the new resonance circuit resonates at a resonance point 1 (resonance frequency fr1). When the power feeding LC resonance circuit 300 resonates, the feeding coil L2 generates an AC magnetic field of the resonance frequency fr1. The power receiving LC resonance circuit 302 constituting a part of the new resonance circuit also resonates by receiving the AC magnetic field. When the power feeding LC resonance circuit 300 and power receiving LC resonance circuit 302 resonate at the same resonance frequency fr1, wireless power feeding from the feeding coil L2 to receiving coil L3 is performed with the maximum power transmission efficiency. Received power is taken from a load LD of the wireless power receiver 118 as output power. Note that the new resonance circuit can resonate not only at the resonance point 1 (resonance frequency fr1) but also at a resonance point 2 (resonance frequency fr2).

FIG. 2 is an exemplary view of the wireless power transmission system 100 capable of feeding power to the wireless power receiver 118 which is moving. A plurality of wireless power feeders 116 a, 116 b, . . . , are buried in a passage such as road or rail. In the feeding coil circuit 120 of the wireless power feeder 116, a plurality of the feeding coils L2 are connected in series to one capacitor C2. In FIG. 2, one feeding coil circuit 120 includes two feeding coils L2. A feeding coil circuit 120 a of the wireless power feeder 116 a includes feeding coils L2 a 1 and L2 a 2 and a capacitor C2 a, and a feeding coil circuit 120 b of the wireless power feeder 116 b includes feeding coils L2 b 1 and L2 b 2 and a capacitor C2 b.

In the wireless power feeder 116 a, a power feeding source VGa supplies AC power to an exciting coil L1 a, and the exciting coil L1 a supplies the AC power to the two feeding coils L2 a 1 and L2 a 2. Then, the AC power is supplied from the feeding coils L2 a 1 and L2 a 2 to the receiving coil L3 and, finally, to the load LD of the wireless power receiver 118. In the wireless power feeder 116 b, AC power is supplied from a power feeding source VGb.

The wireless power receiver 118 is mounted on a moving object such as a vehicle or an electric train. The load LD is a secondary battery such as a lithium ion secondary battery and is charged with power to be supplied from the plurality of buried wireless power feeders 116 a and 116 b. The wireless power feeders 116 are arranged in a moving direction (x-direction) of the wireless power receiver 118. When the wireless power receiver 118 is positioned just above the wireless power feeder 116 a, the wireless power receiver 118 receives power from both or one of the feeding coils L2 a 1 and L2 a 2. When the wireless power receiver 118 moves and reaches a position just above the wireless power feeder 116 b, the wireless power receiver 118 receives power from both or one of the feeding coils L2 b 1 and L2 b 2. With such a configuration, the moving object having the wireless power receiver 118 continuously receives power by wireless from the wireless power feeders 116 buried in the ground while moving.

In the wireless power feeder 116, the feeding coil circuit 120 and power supply circuit 110 are physically separated from each other. Thus, even after the power supply circuit 110 is buried, installation and replacement of the feeding coil circuit 120 can be easily performed. Thus, the power supply circuit 110 and feeding coil circuit 120 need not directly be connected to each other, eliminating the need to strictly specify the size or installation position of the feeding coil circuit 120.

FIG. 3 is a view illustrating an overlapping structure of the feeding coils L2. The two feeding coils L2 a 1 and L2 a 2 included in the feeding coil circuit 120 a are adjacently arranged such that coil surfaces thereof partly overlap each other. Similarly, the feeding coil L2 a 2 of the feeding coil circuit 120 a and feeding coil L2 b 1 of the feeding coil circuit 120 b arranged adjacent to the feeding coil circuit 120 a are arranged such that coil surfaces thereof partly overlap each other. That is, in x-direction (moving direction), the plurality of feeding coils L2 are tightly arranged so as to partially overlap each other. Thus, the wireless power receiver 118 can continuously and stably receive power while moving. The plurality of feeding coils L2 preferably have the same coil area but need not have the same shape.

FIG. 4 is an exemplary view illustrating a state where a vehicle 102 having the wireless power receiver 118 receives power while moving. The vehicle 102 is an EV having the wireless power receiver 118. The load LD in the vehicle 102 is a secondary battery. AC power fed from the plurality of feeding coils L2 arranged in the moving direction is received by the receiving coil L3 provided at a lower portion of the vehicle body and charges the secondary battery through the loading coil L4.

FIG. 5 is an exemplary view illustrating a relationship between power to be supplied to the secondary battery and a position of the vehicle 102. A charge characteristic (in overlapping structure) 104 represents an amount of charge (charge efficiency) of the secondary battery per unit time in a case where the feeding coils L2 are arranged in a partially overlapping manner as illustrated in FIG. 3. A charge characteristic (in non-overlapping structure) 106 represents charge efficiency in a case where the feeding coils L2 are arranged not in an overlapping manner but with a predetermined interval therebetween.

In general, it takes a certain time from when power supply to the secondary battery is started to when the charge is actually started. Therefore, in the case where an interval is provided between the feeding coils L2 (charge characteristic (in non-overlapping structure) 106), not only the secondary battery is intermittently charged, but also a time loss occurs when the charging is resumed, significantly reducing overall charge efficiency. On the other hand, in the case where the coil surfaces of the feeding coils L2 are made to partially overlap each other (charge characteristic (in overlapping structure) 104), continuous and stable charge can be achieved to significantly increase the charge efficiency. For example, when a wound coil such as a spiral, loop, or solenoid coil is used as the feeding coil L2, it is preferable to make the adjacent feeding coils L2 overlap each other in a range of 0 to coil winding width (winding width in x-direction) of feeding coil L2. In this case, it is possible to increase an area where power can continuously and stably fed to the wireless power receiver 118. It is more preferable to make the adjacent feeding coils L2 overlap each other in a range of 1×winding width to ½×winding width. In this case, it is possible to suppress a reduction in the charge efficiency of the wireless power receiver 118 in the overlapping area of the feeding coils L2.

FIG. 6 is an exemplary view of the wireless power feeder 116 of a parallel-feeding type. As illustrated in FIG. 6, in the wireless power feeder 116, a plurality of feeding coil circuits 120-1 and 120-2 may be electromagnetically coupled to one power supply circuit 110. The feeding coil circuit 120-1 includes a feeding coil L2-1 and a capacitor C2-1, and feeding coil circuit 120-2 includes a feeding coil L2-2 and a capacitor C2-2. The feeding coils L2-1 and L2-2 are arranged such that coil surface thereof partially overlap each other as illustrated in FIG. 3. It is desirable that resonance frequencies of the feeding coil circuits 120-1 and 120-2 coincide with each other. With this configuration, AC power can be supplied to the plurality of feeding coils L2 by means of one power feeding source VG.

Hereinafter, a configuration as illustrated in FIG. 2 where the plurality of feeding coils L2 are connected to each other in one feeding coil circuit 120 is referred to as “series-feeding type”, and a configuration as illustrated in FIG. 6 where the plurality of feeding coil circuits 120 are provided for one power supply circuit 110 is referred to as “parallel-feeding type”. The series-feeding type and parallel-feeding type may be combined with each other. That is, a configuration may be adopted in which a plurality of feeding coil circuits 120 are provided for one power supply circuit 110 (power feeding source VG) and each of the plurality of feeding coil circuits 120 includes a plurality of feeding coils L2.

FIG. 7 is an exemplary view of the wireless power receiver 118 of a series-receiving type. As in the case of the feeding coil L2, a plurality of receiving coils L3 may be arranged so as to partially overlap each other. In FIG. 7, one receiving coil circuit 130 includes a plurality of receiving coils L3-1 and L3-2. This configuration is referred to as “series-receiving type”. The receiving coils L3-1 and L3-2 are arranged such that coil surfaces thereof partially overlap each other.

FIG. 8 is an exemplary view of the wireless power receiver 118 of the parallel-receiving type. As illustrated in FIG. 8, a plurality of receiving coil circuits 130-1 and 130-2 may be electromagnetically coupled to one loading circuit 140. This configuration is referred to as “parallel-receiving type”. The receiving coils L3-1 and L3-2 are also arranged such that coil surface thereof partially overlap each other.

There may be a many-to-one relationship, many-to-many relationship or one-to-many relationship between the number of the feeding coils L2 and that of the receiving coils L3. Further, the series-feeding type, parallel-feeding type, series-receiving type, and parallel-receiving type may arbitrarily be combined. In order to change a system configuration, it is only necessary to replace the feeding coil circuit 120 and receiving coil circuit 130 with the power supply circuit 110 and loading circuit 140 remaining unchanged. This is because the receiving coil circuit 130 and loading circuit 140, and the power supply circuit 110 and feeding coil circuit 120 are each coupled to each other electromagnetically but not coupled physically.

FIG. 9 is an exemplary view illustrating a positional relationship between the receiving coil L3 of the wireless power receiver 118 and feeding coil L2 of the wireless power feeder 116. The vehicle 102 having the wireless power receiver 118 moves in x-direction. The plurality of feeding coils L2 are adjacently arranged in x-direction. The wireless power receiver 118, which is of the series-receiving type or parallel-receiving type, and the plurality of receiving coils L3 are arranged in y-direction perpendicular to the moving direction (x-direction). When the arrangement direction (x-direction) of the feeding coils L2 and arrangement direction (y-direction) of the receiving coil L3 are made to be perpendicular to each other as illustrated in FIG. 9, a positional relationship in which the feeding coils L2 and receiving coils L3 face each other is easily maintained even if the vehicle 102 is somewhat displaced in y-direction. Thus, more stable wireless power feeding can be achieved.

Second Embodiment

FIG. 10 is a view illustrating operation principle of a wireless power transmission system 100 according to a second embodiment. The wireless power transmission system 100 according to the second embodiment includes a wireless power feeder 116 and a wireless power receiver 118. The wireless power feeder 116 includes a power feeding LC resonance circuit 300. The wireless power receiver 118 includes a receiving coil circuit 130 and a loading circuit 140. A power receiving LC resonance circuit 302 is formed by the receiving coil circuit 130.

In the second embodiment, the wireless power feeder 116 has the same configuration as that of the wireless power feeder 116 of the first embodiment except that it does not have the exciting coil L1. When the power feeding source VG supplies AC power to the power feeding LC resonance circuit 300 at a resonance frequency fr1, the power feeding LC resonance circuit 300 resonates at a resonance point 1 (resonance frequency fr1).

Third Embodiment

FIG. 11 is a view illustrating operation principle of the wireless power transmission system 100 according to a third embodiment. The wireless power transmission system 100 of the third embodiment also includes the wireless power feeder 116 and wireless power receiver 118. However, the wireless power receiver 118 includes the power receiving LC resonance circuit 302, while the wireless power feeder 116 does not include the power feeding LC resonance circuit 300. That is, the feeding coil L2 does not constitute a part of the LC resonance circuit. More specifically, the feeding coil L2 does not form any resonance circuit with other circuit elements included in the wireless power feeder 116. No capacitor is connected in series or in parallel to the feeding coil L2. Thus, the feeding coil L2 does not resonate in a frequency at which power transmission is performed.

The power feeding source VG supplies AC current of the resonance frequency fr1 to the feeding coil L2. The feeding coil L2 does not resonate but generates an AC magnetic field of the resonance frequency fr1. The power receiving LC resonance circuit 302 resonates by receiving the AC magnetic field. As a result, high AC current flows in the power receiving LC resonance circuit 302. Studies have revealed that formation of the LC resonance circuit is not essential in the wireless power feeder 116. The feeding coil L2 does not constitute a part of the power feeding LC resonance circuit, so that the wireless power feeder 116 does not resonate at the resonance frequency fr1. It has been generally understood that, in the wireless power feeding of a magnetic field resonance type, making resonance circuits which are formed on the power feeding side and power receiving side resonate at the same resonance frequency fr1 (=fr0) allows power feeding of high power. However, it is found that even in the case where the wireless power feeder 116 does not contain the power feeding LC resonance circuit 300, if the wireless power receiver 118 includes the power receiving LC resonance circuit 302, the wireless power feeding of a magnetic field resonance type can be achieved.

Even when the feeding coil L2 and receiving coil L3 are magnetic-field coupled to each other, anew resonance circuit (new resonance circuit formed by coupling of resonance circuits) is not formed due to absence of the capacitor C2. In this case, the stronger the magnetic field coupling between the feeding coil L2 and receiving coil L3, the greater the influence exerted on the resonance frequency of the power receiving LC resonance circuit 302. By supplying AC current of this resonance frequency, i.e., resonance frequency near fr1 to the feeding coil L2, the wireless power feeding of a magnetic field resonance type can be achieved. In this configuration, the capacitor C2 need not be provided, which is advantageous in terms of size and cost.

FIG. 12 is an exemplary view of the wireless power feeder 116 in which a plurality of feeding methods can be switched therebetween. The wireless power feeder 116 illustrated in FIG. 12 has switches SW1 to SW3. The power transmission control circuit 200 is a frequency-changeable power feeding source VG. Hereinafter, the power feeding method of the first embodiment is refereed to as “first feeding type”, power feeding method of the second embodiment is refereed to as “second feeding type”, and power feeding method of the third embodiment is refereed to as “third feeding type”. The wireless power feeder 116 of FIG. 12 controls the switches SW1 to SW3 to switch the feeding type between the first to third feeding types.

(1) First Feeding Type

The power supply circuit 110 including the exciting coil L1 and power feeding source VG (power transmission control circuit 200), and feeding coil circuit 120 including the feeding coil L2 and capacitor C2 are electromagnetically coupled. To this end, the switch SW1 is turned ON, the switch SW2 is connected to a P2 terminal, and the switch SW3 is connected to a P3 terminal. The turning ON of the switch SW1 allows the power supply circuit 110 to be connected to the power transmission control circuit 200. The connection of the switch SW2 to the P2 terminal allows the power feeding coil L2-1, power feeding coil L2-2, and capacitor C2 to be connected in series to each other in the feeding coil circuit 120. The connection of the switch SW3 to the P3 terminal allows the feeding coil circuit 120 to be separated from the power transmission control circuit 200.

(2) Second Feeding Type

In the wireless power feeder 116, the feeding coil L2, capacitor C2, and power feeding source VG are connected in series. The exciting coil L1 is not used. To this end, the switch SW1 is turned OFF, the switch SW2 is connected to the P2 terminal, and the switch SW3 is connected to a P4 terminal. The turning OFF of the switch SW1 disables the use of the power supply circuit 110. The connection of the switch SW2 to the P2 terminal allows the power feeding coil L2-1, power feeding coil L2-2, and capacitor C2 to be connected in series to each other in the feeding coil circuit 120. The connection of the switch SW3 to the P4 terminal allows the feeding coil circuit 120 to be connected to the power transmission control circuit 200.

(3) Third Feeding Type

In the wireless power feeder 116, the feeding coil L2 and power feeding source VG are connected in series to each other. The exciting coil L1 and capacitor C2 are not used. To this end, the switch SW1 is turned OFF, the switch SW2 is connected to the P1 terminal, and the switch SW3 is connected to the P4 terminal. The turning OFF of the switch SW1 disables the use of the power supply circuit 110. The connection of the switch SW2 to the P1 terminal also disables the use of the capacitor C2. The connection of the switch SW3 to the P4 terminal allows the feeding coil circuit 120 to be connected to the power transmission control circuit 200.

In principle, a feeding type exhibiting the maximum power transmission efficiency is selected from among the first to third feeding types. Which one of the first to third feeding types is to be selected may previously be set depending on attribute conditions, such as environmental conditions (temperature, humidity, etc.), vehicle height, and type of a battery, of the moving object. Alternatively, the vehicle 102 may positively specify the feeding type through a communication means. Alternatively, the following configuration may be adopted. That is, when a plurality of wireless power feeder 116 are buried in the road, the wireless power feeders 116 located at first to third stages feed power in the first to third feeding types, respectively, and a feeding type that has exhibited the highest power transmission efficiency among the first to third feeding types is set in the wireless power feeders 116 at the fourth and subsequent stages. In addition to the feeding type, a voltage value or a frequency of power to be fed may be switched.

The wireless power transmission system 100 has been described based on the embodiments. In all of the above embodiments, the plurality of feeding coils L2 are arranged such that the coil surfaces thereof partially overlap each other, power can be fed efficiently, continuously, and stably to the wireless power receiver 118 which is moving. Further, one power feeding source VG is associated with the plurality of feeding coils L2, so that the number of the power feeding source VG can be suppressed even when a large number of the feeding coils L2 need to be arranged. Although one power feeding source VG is used to drive the two feeding coils L2 has been described in the above embodiments, a configuration may be possible in which one power feeding source VG is used to drive three to several tens of the feeding coils L2. Further, in the first embodiment, the power supply circuit 110 and wireless power feeder 116 are physically separated. This advantageously facilitates installation, modification, and the like of the wireless power feeder 116.

The present invention has been described based on the above embodiments. It should be understood by those skilled in the art that the above embodiments are merely exemplary of the invention, various modifications and changes may be made within the scope of the claims of the present invention, and all such variations may be included within the scope of the claims of the present invention. Thus, the descriptions and drawings in this specification should be considered as not restrictive but illustrative.

The “AC power” used in the wireless power transmission system 100 may be transmitted not only as an energy but also as a signal. Even in the case where an analog signal or digital signal is fed by wireless, the wireless power feeding method of the present invention may be used.

Although the “magnetic field resonance type” that utilizes a magnetic field resonance phenomenon has been described in the present embodiments, the magnetic field resonance is not essential in the present invention. For example, the present embodiments can be applied to the above-described type A (for short distance) that utilizes the electromagnetic induction, wherein the feeding coil and receiving coil are electromagnetically coupled (inductively coupled) as in the “magnetic field resonance type”. 

1. A wireless power feeder that feeds power by wireless from a feeding coil to a receiving coil, comprising: a plurality of feeding coils; and a power transmission control circuit provided in common to the plurality of feeding coils for supplying AC power thereto, the plurality of feeding coils being adjacently arranged such that coil surfaces thereof partially overlap each other.
 2. The wireless power feeder according to claim 1, further comprising an exciting coil that is magnetically coupled to the plurality of feeding coils and collectively feeds AC power supplied from the power transmission control circuit to the plurality of feeding coils, wherein the power transmission control circuit supplies the AC power to the plurality of feeding coils through the exciting coil.
 3. The wireless power feeder according to claim 1, wherein the plurality of feeding coils are connected in series to each other and are further connected in series to a capacitor to constitute an LC resonance circuit, and the power transmission control circuit supplies the AC power to the LC resonance circuit including the plurality of feeding coils.
 4. The wireless power feeder according to claim 1, wherein the plurality of feeding coils are connected in series to capacitors respectively to constitute a plurality of LC resonance circuits, and the power transmission control circuit supplies the AC power to the plurality of LC resonance circuits.
 5. A wireless power receiver that receives, at a receiving coil, AC power fed by wireless from a feeding coil, comprising: a plurality of receiving coils; and a loading coil provided in common to the plurality of receiving coils, magnetically coupled thereto, and receives the AC power that the plurality of receiving coils have received from the feeding coil, the plurality of receiving coils being adjacently arranged such that coil surfaces thereof partially overlap each other.
 6. The wireless power receiver according to claim 5, wherein the loading coil is connected with a secondary battery, and the secondary battery is charged with the AC power supplied to the loading coil.
 7. The wireless power receiver according to claim 5, wherein the plurality of receiving coils are connected in series to each other and are further connected in series to a capacitor to constitute an LC resonance circuit.
 8. The wireless power receiver according to claim 5, wherein the plurality of receiving coils are connected in series to capacitors respectively to constitute a plurality of LC resonance circuits, and the loading coil collectively receives the AC power from the plurality of LC resonance circuits.
 9. The wireless power receiver according to claim 5, wherein the plurality of receiving coils are arranged in a first direction, and the wireless power receiver is formed so as to be movable in a direction substantially perpendicular to the first direction.
 10. A wireless power transmission system for feeding power from a feeding coil to a receiving coil, comprising: a wireless power feeder; and a wireless power receiver, the wireless power feeder including a plurality of feeding coils and a power transmission control circuit provided in common to the plurality of feeding coils for supplying AC power thereto, the wireless power receiver including a receiving coil, a loading coil that is magnetically coupled to the receiving coil and receives the AC power that the receiving coil has received from the feeding coil, and a secondary battery connected to the loading coil, the plurality of feeding coils being adjacently arranged such that coil surfaces thereof partially overlap each other, the secondary battery being charged with the AC power supplied to the loading coil. 